1. Field of the Invention
The present invention relates generally to a new approach to coronary artery and coronary artery bypass graft imaging, and more particularly to magnetic resonance or computed tomographic angiography following an aortic root injection of contrast (magnetic resonance imaging contrast or iodinated contrast) via a new percutaneously placed catheter. This new approach to coronary artery and coronary artery bypass graft imaging also incorporates a new catheter design and a new ECG-triggered pulsed injection procedure via a power injector. Specifically, the new process of coronary imaging uses a new catheter device and new power injector controller or interface.
2. Background of the Invention
Coronary artery disease remains the leading cause of death worldwide. The diagnosis via the gold standard, cardiac catheterization, remains a time-consuming, expensive, and invasive procedure with some considerable risk. Cardiac catheterization specifically involves arterial puncture, usually in the groin or upper extremity, with a needle through which a guidewire is passed fluoroscopically to the ascending aorta. Over the guidewire, a catheter is inserted and subsequently, the guidewire is removed and iodinated contrast is injected to opacify the aorta. Unfortunately, the vascular-to-background contrast is not sufficient for adequate visualization of the coronary arteries using X-ray angiography. As such, there are different kinds of catheters that are used to engage either the right or left native coronary arteries or bypass vein grafts (FIGS. 4 and 5). This procedure requires separate injections into the coronary arteries or bypass grafts which can induce arrhythmias, require over one-hour of procedural time, requires larger bore catheters, exposes the physician and patient to ionizing radiation and subjects the patient with coronary artery disease to contrast induced nephropathy, especially in cases requiring higher loads of iodinated contrast. An alternative route is certainly welcomed and non-invasive harmonic Doppler, magnetic resonance angiography (MRA) and computed tomographic angiography (CTA) have been applied but without reproducible clinical success and without complete clinical acceptance due to various factors.
Of the non-invasive techniques, MRA and CTA are favored over harmonic Doppler imaging since ultrasound techniques are field-of-view limited and require the insertion of a trans-esophageal probe into the esophagus. On the other hand, the most common limiting factor when employing MRA and CTA is the underlying blood pool which also enhances when contrast enhanced protocols are employed using a peripheral intravenous contrast injection route. This results in a frequent obscuration of the native coronary arteries. As such, the method of the present invention provides an imaging concept of the coronary arteries employing a new catheter device in conjunction with either an MRI or computed tomography (CT) imaging machine.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention places a thin caliber catheter into the ascending aorta as already done for conventional catheter X-ray angiography. The thin catheter is placed over a guidewire following an arterial puncture in the groin (femoral artery) or in the upper extremity (brachial or radial artery). The arterial puncture with thinner caliber catheters is less traumatic to the patient resulting in few complications related to arterial puncture such as arterial venous fistulas, pseudoaneurysms and hemorrhage. This catheter end is three-dimensional (like a coil or spring) and will sit in the ascending aorta at its root and will not be engaged into the native coronary arteries or into the saphenous vein grafts (FIGS. 4 and 5) as with prior X-ray angiography catheterization techniques. One catheter in one location is used to image the ascending aorta, aortic arch and arch vessels as well as the native coronary arteries and coronary artery bypass grafts employing either contrast enhanced MRA or contrast enhanced CTA. As such, conventional X-ray angiography may be replaced with the minimally invasive catheter enhanced MRA or CTA procedures. To conduct a similar procedure employing a catheter in the ascending aorta and contrast enhanced X-ray angiography would not yield sufficient vascular-to-background contrast of the native coronary arteries nor of the coronary artery bypass grafts. The soft tissue contrast resolution with MRA and CTA is, however, far superior to X-ray angiography. Furthermore, the contrast injection protocol calls for a new method of delivery of contrast material via the catheter.
Although one may continuously inject contrast via a power injector or by hand injection with a syringe, the present invention provides pulsed injection technique which delivers contrast material during the diastolic phase of the cardiac cycle when there is more perfusion taking place to the epicardial coronary artery circulation. This technique not only enhances the delivery of contrast to the coronary arteries, but also reduces the amount of contrast required for coronary MRA or CTA. An external monitor is employed to acquire a noise free ECG signal. From the QRS complex or R-wave of the ECG signal, the power injector is triggered via an interface to inject contrast at a specified injection rate after a predetermined delay time which drives the injection time interval into the diastolic phase of the cardiac cycle. The injection time interval may be predetermined to allow for an end to the injection prior to the next R-wave of the ECG signal or can be simultaneously terminated and then immediately reactivated to begin injection following the predetermined delay time when the next QRS complex arrives. Once another R-wave of the ECG signal appears, the process is repeated until the entire volume of contrast is completely utilized.
This new procedure would obviate the risks and complications of arterial puncture with larger catheters, obviates the risks of arrhythmias from direct engagement of the coronary arteries and provides high vascular-to-background contrast, which are well known with MRA and CTA. Furthermore, the vascular bed and myocardium will enhance without obscuration from the underlying blood pool, which ordinarily enhances when a peripheral injection of contrast is made. As such, the native coronary arteries and coronary artery bypass grafts are visualized free from the underlying blood pool. They are imaged employing breath hold first pass MRA or CTA imaging with either the MRI or CT machine. Furthermore, given the tomographic capabilities of MRI and CT, myocardial perfusion imaging is possible by re-injecting the patient after pharmocologic or exercise stress. This will show additional findings, which are of clinical importance, such as the extent of myocardium that is in jeopardy or at risk. As such, this one procedure will diagnose the presence or absence of disease of the coronary arteries or coronary artery bypass grafts as well as the significance of any flow constricting disease identified on coronary imaging. As a result, this one technique has the potential of replacing diagnostic cardiac catheterization and also has the potential of replacing myocardial scintigraphy. This one technique has the potential to replace these two procedures at a fraction of the cost. Although one would prefer MRA over CTA given the lack of ionizing radiation, CTA can provide similar results but at the expense of nephrotoxic iodinated contrast agents and ionizing radiation. CTA protocols will require the use of new generation multislice helical/spiral ECG-triggered scan acquisitions, which capture the coronary arteries with a temporal resolution of 250 msecs or less per imaging slice.